Imaging the internal spin structures of skyrmions by Lorentz scanning transmission electron microscopy*

Magnetic skyrmions are noncollinear spin textures that have been detected and studied using many different techniques. However, a detailed characterization of the internal spin structures of skyrmions, especially for skyrmions with diameters smaller than 100 nm, is experimentally challenging. These experiments are extremely important for defining the chirality and spin topology. Recent experiments show that Lorentz scanning transmission electron microscopy with a high-dynamic-range pixel array detector - Lorentz 4D-STEM, allows direct imaging of magnetic structures at a spatial resolution down to a few nanometers. Here we first show that Lorentz 4D-STEM technique combining with ptychography can be used to detect the detailed spin structures inside skyrmions and spin singularities in skyrmion lattices. We subsequently demonstrate the direct determination of the chirality of Néel-type skyrmions from the magnetic induction field distribution in an inclined sample setup. Using both fast, wide-field Lorentz TEM and quantitative, high-resolution Lorentz STEM, we are able to perform real-space imaging of magnetic spin textures at length scales that span microns down to a few nanometers.